This patent application relates to improvements to the performance of U.S. Pat. No. 5,816,315 of Stark, dated Oct. 6, 1998, which teaches a two pass opposed (reverse) flow cooling coil with uniform heat transfer Media serving each pass) one pass of coolant flow being parallel to airflow and the other pass of coolant flow being counter to airflow.
Finned-tube coils used for air cooling and dehumidifying are typically selected based on thermal performance. A given set of inlet temperature and humidity conditions are cooled to a given set of outlet temperature and humidity conditions.
The terms “counter-flow” and “parallel-flow” refer to temperature flow (Thermal) rather than fluid flow.
Unlike water cooling coils, in refrigerant cooling coils the refrigerant temperature drops, relative to its pressure drop, as it moves through the coil. Therefore, the fluid flow in a refrigerant coil is parallel to airflow, while the temperature is counter-flow.
“Counter-flow” is defined as the flow pattern where the air temperature drop flows counter (opposite direction) to the fluid temperature rise. This is also referred to as “Thermal” counter-flow.
“Parallel-flow” is defined as the flow pattern where the air temperature drop flows parallel (same direction) to the fluid temperature rise. This is also referred to as “Thermal” parallel-flow.
Air travels either parallel or counter, relative to tube side coolant flow.
The parallel-flow pass is known to be the least efficient but nevertheless contributes to improving the overall thermal performance, while disimproving overall air pressure drop.
Fins for finned tube heat exchangers can vary in style, density, thickness and depth. Examples of fin styles are flat, corrugated and louvered. Fin styles can improve performance by creating turbulence. The best styles improve heat transfer with minimal impact on pressure drop. Fin density is the number of fins per inch (FPI). Increasing fin density improves heat transfer by increasing heat transfer surface; they also occupy more space in the direction of airflow, thereby increasing air velocity and turbulence. Fin thickness relates to turbulence because thicker fins occupy more space in the direction of airflow, thereby increasing air velocity and turbulence. Fin depth is related to the number of rows in a coil, which increases or decreases the finned surface area. Collectively, the various combinations of fin style, density, thickness and depth are referred to herein as “Finned Media Configuration”. Improving or disimproving “Finned Media” refers to Improving or disimproving pressure drop, heat transfer, both or a combination.
Air pressure drop occurs as it travels through the finned media. This pressure drop increases or decreases the fan power needed to move air through the process.
Pressure drop and heat transfer are related in the sense that greater pressure drop generally results in greater heat transfer. However, pressure drop in a parallel-flow pass is less effective on overall heat transfer, when compared with pressure drop in a counter-flow pass.
A value could be expressed as unit of heat transfer/unit of pressure drop (BTU/Inch water column). When the value in the parallel-flow sections result in a value approaching the counter-flow sections, the Finned Media in both passes are optimized. This technique would be incorporated into the overall system design phase of dual-pass installations benefitting from this invention.